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論文

Massive Dirac magnons in the three-dimensional honeycomb magnetic oxide FeTiO

Chung, J.-H.*; Kwangwoo, S.*; Yokoo, Tetsuya R.; 植田大地*; 今井正樹; Kim, H.-S.; Kiem, D. H.; Han, M. J.*; 社本真一

Scientific Reports (Internet), 15, p.5978_1 - 5978_10, 2025/02

https://doi.org/10.1038/s41598-025-90478-2

被引用回数：0

Two dimensional honeycomb ferromagnets host massless Dirac magnons which are a bosonic analogue of Dirac fermions in graphene. The Dirac magnons may become massive and topological when the timereversal symmetry breaks and an energy gap opens up at the Dirac point, which was experimentally observed in Cr $^{3+}$ -based van der Waals magnets. Here, we investigate the spin wave excitations in the magnetic oxide FeTiO with Fe $^{2+}$ electrons (). Using inelastic neutron scattering, we observe two magnon bands separated by a 1.2-meV gap at the Dirac points indicating that its Dirac magnons are massive. Using the linear spin-wave and density functional theory calculations, we find that the spin-orbit-coupled antisymmetric Dzyaloshinskii-Moriya exchanges can best account for the observed Dirac gap opening. The associated Berry curvature and Chern number () indicate that FeTiO hosts topological spin excitations via time-reversal symmetry breaking of Dirac magnons.

論文

Full-f gyrokinetic simulations of hydrogen isotope mixing in tokamak plasmas

井戸村泰宏

Physics of Plasmas, 31(10), p.102504_1 - 102504_10, 2024/10

https://doi.org/10.1063/5.0229513

被引用回数：0 パーセンタイル：0.00(Physics, Fluids & Plasmas)

トカマクプラズマにおける水素同位体混合現象をfull-fジャイロ運動論シミュレーションを用いて解析した。モデルプラズマのパラメータは、重水素(D)ペレットを水素(H)プラズマに入射した後にエネルギー閉じ込め時間スケールで水素同位体混合が発生したJETの水素同位体ペレット実験に基づいて選択した。重水素ペレット入射前後のプラズマ分布を用いて2つの数値実験を行った。どちらの場合も、炉心の乱流揺動はイオン温度勾配駆動乱流によって特徴づけられるが、後者の場合、外側の領域に捕捉電子モード乱流が存在する。前者の場合、バルクHイオンの密度分布は準定常状態に保たれ、その粒子閉じ込め時間はエネルギー閉じ込め時間よりも一桁長い。後者の場合、バルクHイオンとペレットDイオンの密度分布は、エネルギー閉じ込め時間の時間スケールで過渡的な緩和を示し、早い水素同位体混合を示す。トロイダル角運動量バランスから、水素同位体混合はトロイダル電場応力によって駆動されることがわかった。

論文

薄膜の垂直磁気異方性

高梨弘毅; 関剛斎*

まぐね, 19(3), p.100 - 106, 2024/06

薄膜の垂直磁気異方性は、磁気記録のみならずスピントロニクスにおいても重要な役割を果たしている。本解説記事では、垂直磁気異方性に関して、磁気多層膜、規則合金膜、希土類遷移金属アモルファス合金多層膜、不均一膜やグラニュラー膜など、垂直磁化を持つ具体例を示しながら、基礎からこれまでの研究、そして最近の研究動向を概説する。それぞれの具体例について、構造対称性の破れによる界面磁気異方性、ひずみによる磁気弾性異方性、バルクの結晶磁気異方性、原子の方向性規則配列などの垂直磁気異方性の物理的起源を議論する。

論文

Convection and joint characteristics in aluminum alloy melting zone during resistance spot welding of dissimilar Fe-Al material in external magnetic field

船引雄太*; 伊與田宗慶*; 菖蒲敬久; 松田朋己*; 林雄二郎*; 佐野智一*; 他8名*

Journal of Manufacturing Processes, 115, p.40 - 55, 2024/04

https://doi.org/10.1016/j.jmapro.2024.01.049

被引用回数：2 パーセンタイル：56.70(Engineering, Manufacturing)

In resistance spot welding (RSW) of Fe and Al alloy, an intermetallic compound (IMC) is formed at the joining interface, and it is known that the joining strength of the joint decreases as the IMC becomes thicker. In this study, the convection behavior in the Al alloy melting zone of an Fe-Al alloy RSW was varied and the effect on the joint characteristics was investigated. For this study, focusing on the electromagnetic force generated in the Al alloy melting zone, the convection behavior in the Al alloy melting zone was changed by adding an external magnetic field using neodymium magnets. In-situ evaluation of the convection behavior using synchrotron radiation and cross-sectional macro-observation of the joint revealed that the addition of an external magnetic field causes a non-axisymmetric change in the convection behavior in the Al alloy melting zone, which results in the deflection of the Al alloy melting zone. The addition of an external magnetic field increases the driving force of convection and homogenizes the temperature field at the joining interface, suggesting that the IMC near the center is formed thin and uniform. Furthermore, from the cross tension test and the observation of the fracture surface of the joint after the test, it was clarified that the CTS of the joint with an external magnetic field was improved by the propagation of cracks into the Al alloy melting zone during the test.

論文

Uniaxial magnetic anisotropy of L1 $_{0}$ -FeNi films with island structures on LaAlO $_{3}$ (110) substrates by nitrogen insertion and topotactic extraction

西尾隆宏*; 伊藤啓太*; 藏裕彰*; 高梨弘毅; 柳原英人*

Journal of Alloys and Compounds, 976, p.172992_1 - 172992_8, 2024/03

https://doi.org/10.1016/j.jallcom.2023.172992

被引用回数：2 パーセンタイル：30.94(Chemistry, Physical)

Tetrataenite (L1 $_{0}$ -FeNi) has potential for application in next-generation permanent magnets. This compound is a rare-earth-free material comprising Fe and Ni, which are abundant elements. In addition, an extremely high uniaxial magnetocrystalline anisotropy (u) is expected for L1 $_{0}$ -FeNi because of the ordered arrangement of the elements. This study reports the magnetic properties of uniaxially oriented L1 $_{0}$ -FeNi films with island structures fabricated by a novel method involving the radio-frequency sputter deposition of FeNi alloy films onto a LaAlO $_{3}$ (110) substrate, followed by nitrogen insertion and topotactic extraction. FeNiN(110) films are epitaxially grown on the LAO(110) plane by the nitriding and additional annealing process of the FeNi alloy films at high temperatures under ammonia gas to reduce the volume fraction of crystallographic variants. Uniaxially oriented L1 $_{0}$ -FeNi alloy films with island structures are obtained after the topotactic denitriding of the FeNiN films. The uniaxial magnetic anisotropy of the L1 $_{0}$ -FeNi films is determined from the magnetization curves and via magnetic torque measurements of the films. The obtained L1 $_{0}$ -FeNi film exhibiting a relatively high superlattice order parameter of 0.74 yielded a uniaxial magnetocrystalline anisotropy energy of ~0.63 MJ/m $^{3}$ at 300 K, as well as coercivities of 319 and 358 kA/m at 300 and 10 K, respectively. This coercivity is the highest value reported for artificial L1 $_{0}$ -FeNi to date.

論文

Quantum critical behavior of the hyperkagome magnet MnCoSi

山内宏樹; Sari, D. P.*; 安井幸夫*; 坂倉輝俊*; 木村宏之*; 中尾朗子*; 大原高志; 本田孝志*; 樹神克明; 井川直樹; et al.

Physical Review Research (Internet), 6(1), p.013144_1 - 013144_9, 2024/02

https://doi.org/10.1103/PhysRevResearch.6.013144

-Mn-type family alloys Mn have three-dimensional antiferromagnetic (AFM) corner-shared triangular network. The antiferromagnet MnRhSi shows magnetic short-range order (SRO) over a wide temperature range of approximately 500 K above the Nel temperature $T_{rm N}$ = 190 K. MnCoSi has the smallest lattice parameter and the lowest $T_{rm N}$ in the family compounds. The quantum critical point (QCP) from AFM to the quantum paramagnetic state is expected near a cubic lattice parameter of 6.15 of MnCoSi is only 140 K, quantum critical behavior is observed in MnCoSi as the enhancement of the electronic specific heat coefficient . We study how the magnetic SRO appears in MnCoSi by using neutron scattering, SR, and physical property measurements. The experimental results show that the neutron scattering intensity of the magnetic SRO does not change much regardless of the suppressed magnetic moment in the long-range magnetic ordered state compared to those of MnRhSi. The initial asymmetry drop ratio of SR above $T_{rm N}$ becomes small, and the magnetic SRO temperature $T_{SRO}$ is suppressed to 240 K. The results suggest that the MnCoSi is close to the QCP in the Mn system.

論文

Magnetic layer thickness influence on magnetoelastic properties anisotropy in Co $_{2}$ Fe $_{0.4}$ Mn $_{0.6}$ Si heusler alloy thin films

Nabialek, A.*; Chumak, O.*; 関剛斎*; 高梨弘毅; Baczewski, L. T.*; Szymczak, H.*

IEEE Transactions on Magnetics, 59(11), p.2501405_1 - 2501405_5, 2023/11

https://doi.org/10.1109/TMAG.2023.3287324

被引用回数：2 パーセンタイル：20.26(Engineering, Electrical & Electronic)

The anisotropic magnetoelastic (ME) properties of epitaxial Co $_{2}$ Fe $_{0.4}$ Mn $_{0.6}$ Si(CFMS) Heusler alloy thin films with thicknesses ranging from 8 to 100 nm were investigated using the strain-modulated ferromagnetic resonance (SMFMR) technique. The calculation of the first cubic magnetocrystalline (MC) constant $_{1}$ and the two cubic ME constants $_{1}$ and $_{2}$ was carried out assuming the cubic symmetry of the magnetic layer. A significant negative perpendicular MC anisotropy, of the order of 10 $^{5}$ J/m $^{3}$ , was also observed. The investigated parameters were found to be dependent on the thickness of the magnetic layer. The thinnest magnetic layers showed the strongest cubic MC anisotropy and the weakest anisotropy of ME properties. These findings highlight the importance of considering the magnetic layer thickness when evaluating the anisotropy in the ME properties of Heusler alloy thin films.

論文

Elucidation of solid particle interfacial phenomena in liquid sodium; Magnetic interactions on liquid metal and solid atoms at the solid interface

Tei, C.; 大高雅彦; 桑原大介*

Chemical Physics Letters, 829, p.140755_1 - 140755_6, 2023/10

https://doi.org/10.1016/j.cplett.2023.140755

被引用回数：1 パーセンタイル：16.60(Chemistry, Physical)

固体金属粒子の界面に付着した液体ナトリウムの核磁気共鳴(NMR)信号を初めて検出することに成功した。本研究では、液体ナトリウムと液体ナトリウム中に浮遊する金属粒子との相互作用の違いによる緩和時間の違いを確認した。その結果、微小チタン粒子表面と液体金属ナトリウムは化学的ではなく物理的に相互作用していることが明らかとなった。

論文

Antiferromagnetic films and their applications

廣畑貴文*; Lloyd, D. C.*; 窪田崇秀*; 関剛斎*; 高梨弘毅; 介川裕章*; Wen, Z.*; 三谷誠司*; 小泉洸生*

IEEE Access, 11, p.117443 - 117459, 2023/10

https://doi.org/10.1109/ACCESS.2023.3326448

被引用回数：2 パーセンタイル：19.73(Computer Science, Information Systems)

Spintronic devices are expected to replace the recent nanoelectronic memories and sensors due to their efficiency in energy consumption and functionality with scalability. To date, spintronic devices, namely magnetoresistive junctions, employ ferromagnetic materials by storing information bits as their magnetization directions. However, in order to achieve further miniaturization with maintaining and/or improving their efficiency and functionality, new materials development is required: 1) increase in spin polarization of a ferromagnet or 2) replacement of a ferromagnet by an antiferromagnet. Antiferromagnetic materials have been used to induce an exchange bias to the neighboring ferromagnet but they have recently been found to demonstrate a 100% spin-polarized electrical current, up to THz oscillation and topological effects. In this review, the recent development of three types of antiferromagnets is summarized with offering their future perspectives towards device applications.

論文

Spontaneous topological Hall effect induced by non-coplanar antiferromagnetic order in intercalated van der Waals materials

高木寛貴*; 高木里奈*; 見波将*; 野本拓也*; 大石一城*; 鈴木通人*; 柳有起*; 平山元昭*; Khanh, N.*; 軽部皓介*; et al.

Nature Physics, 19(7), p.961 - 968, 2023/07

https://doi.org/10.1038/s41567-023-02017-3

被引用回数：37 パーセンタイル：98.82(Physics, Multidisciplinary)

In ferromagnets, electric current generally induces a transverse Hall voltage in proportion to the internal magnetization. This effect is frequently used for electrical readout of the spin up and down states. While these properties are usually not expected in antiferromagnets, recent theoretical studies predicted that non-coplanar antiferromagnetic order with finite scalar spin chirality - meaning a solid angle spanned by neighboring spins - can induce a large spontaneous Hall effect even without net magnetization or external magnetic field. This phenomenon, the spontaneous topological Hall effect, can potentially be used for the efficient electrical readout of the antiferromagnetic states, but it has not been experimentally verified due to a lack of appropriate materials hosting such magnetism. Here, we report the discovery of all-in-all-out type non-coplanar antiferromagnetic order in triangular lattice compounds CoTa $_{3}$ S $_{6}$ and CoNb $_{3}$ S $_{6}$ . These compounds are reported to host unconventionally large spontaneous Hall effect despite their vanishingly small net magnetization, and our analysis reveals that it can be explained in terms of the topological Hall effect that originates from the fictitious magnetic field associated with scalar spin chirality. These results indicate that the scalar spin chirality mechanism offers a promising route to the realisation of giant spontaneous Hall response even in compensated antiferromagnets, and highlight intercalated van der Waals magnets as a promising quasi-two-dimensional material platform to enable various nontrivial ways of electrical reading and possible writing of non-coplanar antiferromagnetic domains.

論文

Short-range spin order in paramagnetic AgCrSe $_{2}$

中村惇平*; 川北至信; 岡部博孝*; Li, B.*; 下村浩一郎*; 末益崇*

Journal of Physics and Chemistry of Solids, 175, p.111199_1 - 111199_8, 2023/04

https://doi.org/10.1016/j.jpcs.2022.111199

被引用回数：2 パーセンタイル：16.48(Chemistry, Multidisciplinary)

Muon spin rotation (SR) experiments were performed to directly investigate the temperature dependence of the short-range order or correlations of chromium spins in the paramagnetic phase of AgCrSe $_{2}$ . The detailed investigation of the SR spectra over a wide temperature range from low to high temperatures revealed that the short-range spin correlations developed below about 184 K. It also confirmed no short-range correlations at high temperatures, which had been controversial in previous quasi-elastic neutron scattering studies. In addition, the muon spin relaxation was qualitatively changed and showed large missing asymmetry below about 89 K, where the correlation clearly implied short-range spin order. There could be a preparative phenomenon of the phase transition or an anisotropic short-range spin correlation.

論文

Ferromagnetic crossover within the ferromagnetic order of U $_{7}$ Te $_{12}$

Opletal, P.; 酒井宏典; 芳賀芳範; 常盤欣文; 山本悦嗣; 神戸振作; 徳永陽

Journal of the Physical Society of Japan, 92(3), p.034704_1 - 034704_5, 2023/03

https://doi.org/10.7566/JPSJ.92.034704

被引用回数：1 パーセンタイル：27.58(Physics, Multidisciplinary)

U $_{7}$ Te $_{12}$ の単結晶の物理的性質を調べた。U $_{7}$ Te $_{12}$ が3つの非等価な結晶ウランサイトを持つ六方晶構造を持つことを確認した。常磁性モーメントは、すべてのサイトで一様なモーメントを仮定すると、ウランサイトあたり約1 $mu_{B}$ と推定される。強磁性相転移は $T_{rm C}$ =48Kで発生し、面内磁化は急激に増加するが、面外成分はあまり増加しない。磁場冷却条件下で温度がさらに $T_{rm C}$ 以下に低下すると、面外成分はT $^{star}$ =26K付近で急激に増加する。対照的に、T $^{star}$ 付近で面内成分はほとんど変化しない。比熱測定では、T $^{star}$ 付近に型の異常がないことが示されているため、これらの振る舞いは、秩序した磁気モーメントの再配向、もしくは複数のウランサイトの連続した逐次磁気転移を示唆している。

論文

Magnetic properties of single crystalline TbSb

北折暁*; 金澤直也*; 木田孝則*; 鳴海康雄*; 萩原政幸*; 金道浩一*; 竹内徹也*; 仲村愛*; 青木大*; 芳賀芳範; et al.

Journal of the Physical Society of Japan, 92(2), p.024702_1 - 024702_6, 2023/02

https://doi.org/10.7566/JPSJ.92.024702

被引用回数：1 パーセンタイル：27.58(Physics, Multidisciplinary)

Magnetic properties of TbSb are reported. Unlike previous investigations on a polycrystal showing multiple phase transitions, the present single crystal sample shows a single transition 133 K. It is also shown that the magnetic hysteresis increases at low temperatures.

論文

Development of a miniature electromagnet probe for the measurement of local velocity in heavy liquid metals

有吉玄; 大林寛生; 佐々敏信

Journal of Nuclear Science and Technology, 59(9), p.1071 - 1088, 2022/09

https://doi.org/10.1080/00223131.2022.2030824

被引用回数：1 パーセンタイル：16.92(Nuclear Science & Technology)

液体重金属中の局所流速計測において、電磁誘導を用いた計測手法は効果的手法の一つである。永久磁石を利用した流速計として、Ricou and Vives' probeやVon Weissenfluh's probeが広く知られているが、これらの流速計は液温上昇に伴う永久磁石の熱減磁により、流速感度および計測体積が低下することが問題点として挙げられる。特に、永久磁石のキュリー温度を超える温度域では流速検出不能となる。そこで本研究では、流速計が持つ温度依存性の解消を目的とし、小型電磁石を内蔵する流速計を開発した。開発された流速計の直径は6mm、長さは155mmである。流速計の基本性能は、室温環境下における矩形管内水銀流れの局所流速分布計測を通して確認され、流速感度および計測体積が評価された。計測された局所流速分布は数値計算によりその妥当性が確認された。

論文

Single crystal growth and magnetic properties of -Mn and -Mn

大貫惇睦*; 青木大*; 仲村愛*; 松田達磨*; 中島美帆*; 芳賀芳範; 竹内徹也*

Journal of the Physical Society of Japan, 91(6), p.065001_1 - 065001_2, 2022/06

https://doi.org/10.7566/JPSJ.91.065001

被引用回数：0 パーセンタイル：0.00(Physics, Multidisciplinary)

Single crystals of -Mn and -Mn are successfully grown. Non-Fermi-liquid relations of the low-temperature resistivity and specific heat are found in the spin-liquid state of -Mn. On the other hand, -Mn exhibits antiferromagnetic transition.

論文

Experimental analysis on dynamics of liquid molecules adjacent to particles in nanofluids

橋本俊輔*; 中島健次; 菊地龍弥*; 蒲沢和也*; 柴田薫; 山田武*

Journal of Molecular Liquids, 342, p.117580_1 - 117580_8, 2021/11

https://doi.org/10.1016/j.molliq.2021.117580

被引用回数：4 パーセンタイル：18.33(Chemistry, Physical)

エチレングリコール水溶液中に二酸化ケイ素(SiO $_{2}$ )ナノ粒子を分散したナノ流体の準弾性中性子散乱測定(QENS)およびパルス磁場勾配核磁気共鳴分析(PFGNMR)を行った。研究目的は、このナノ流体の熱伝導率が理論値を超えて増加するメカニズムを解明することだった。得られた実験結果は、SiO $_{2}$ ナノ粒子の周りの液体分子の運動が非常に制限されているため、SiO $_{2}$ ナノ粒子の添加により、エチレングリコール水溶液中の液体分子の自己拡散係数が低下していることを示す。そして温度一定の条件で、SiO $_{2}$ ナノ流体中で、液体分子の自己拡散係数が減少するにつれて、熱伝導率が増加した。

論文

Probing the long-range structure of the $T^{+}_{cc}$ with the strong and electromagnetic decays

Meng, L.*; Wang, G.-J.*; Wang, B.*; Zhu, S.-L.*

Physical Review D, 104(5), p.L051502_1 - L051502_8, 2021/09

https://doi.org/10.1103/PhysRevD.104.L051502

被引用回数：79 パーセンタイル：98.65(Astronomy & Astrophysics)

最近発見された $T^+_{cc}$ 状態の長距離構造をその強い相互作用と電磁相互作用による崩壊の分岐の様子から推定することが可能であることを示した。その結果、 $T_{cc}$ の主成分は $D^{*+}D^0$ であることがわかった。

論文

Feasibility study of magnetic-domain observation by means of non-resonant magnetic X-ray diffraction

稲見俊哉*; 菖蒲敬久; 石井賢司*

IEEE Transactions on Magnetics, 57(3, Part 2), p.6400105_1 - 6400105_5, 2021/03

https://doi.org/10.1109/TMAG.2020.3046006

被引用回数：0 パーセンタイル：0.00(Engineering, Electrical & Electronic)

Although the observation of magnetic domains well below the surface of a sample appears to be relatively easy, in reality, magnetic domains inside metallic samples have not been investigated in detail due to a lack of adequate techniques. Non-resonant magnetic X-ray diffraction (NRMXRD) is a candidate for such 3-D magnetic microscopy. A relatively small focus size of less than 100 nm and a relatively long attenuation length of more than 100 m can be obtained by using high-energy synchrotron X-rays. However, NRMXRD has a disadvantage in that the magnetic contrast is low. It is known that the magnetic contrast in NRMXRD increases with increasing the total polarization of the incident X-rays. In this feasibility study, we carried out NRMXRD experiments on a metallic iron sample to examine whether the magnetic contrast can be sufficiently enhanced even for high-energy X-rays.

論文

Single-crystal growth and magnetic phase diagram of the enantiopure crystal of NdPtB

佐藤芳樹*; 本多史憲*; Maurya, A.*; 清水悠晴*; 仲村愛*; 本間佳哉*; Li, D.*; 芳賀芳範; 青木大*

Physical Review Materials (Internet), 5(3), p.034411_1 - 034411_9, 2021/03

https://doi.org/10.1103/PhysRevMaterials.5.034411

被引用回数：2 パーセンタイル：9.09(Materials Science, Multidisciplinary)

Single-crystal growth and magnetic properties of NdPtB are reported on a enantiopure crystal. We observed multiple phase transitions at 9.5 and 11 K under zero magnetic field. Nontrivial magnetic phase diagram demonstrates the competitive interactions in this system.

論文

Accelerator design for 1.3-MW beam power operation of the J-PARC Main Ring

五十嵐進*; 野村昌弘; 田村文彦; 山本昌亘; 島田太平; 他49名*

Progress of Theoretical and Experimental Physics (Internet), 2021(3), p.033G01_1 - 033G01_28, 2021/03

https://doi.org/10.1093/ptep/ptab011

被引用回数：8 パーセンタイル：60.40(Physics, Multidisciplinary)

The J-PARC Main Ring (MR) has supplied the high-intensity proton beam for the T2K long- baseline neutrino experiment since 2010. The present beam power is 510 kW and the total number of protons on the target reaches 3.6410 $^{21}$ . To observe charge-conjugation and parity- transformation (CP) violation in the lepton sector with high accuracy, more protons need to be delivered to the T2K target. The project to upgrade the beam power to 1.3 MW started as a mid-term plan of the MR. In parallel to preparing a full technical design report, the technical designs of hardware upgrades using new technologies and all accelerator components that are necessary to deliver the 1.3 MW beam power are summarized and consolidated in this short paper. Further, this paper includes beam dynamics studies and simulation results for handling 3.310 $^{14}$ protons per pulse without significant beam loss in the ring and transport lines.